The present invention particularly but not exclusively relates to a wireless communications device wherein the first integrated circuit comprises a digital baseband chip and the second integrated circuit comprises an analogue baseband chip.
Such a device is known where the first integrated circuit has a processor and a memory connected to the processor. The processor is responsible for the processing functions of the device, which include signal processing of digital samples received from wireless signals which are received and transmitted by the analogue baseband chip. Digital samples from wireless signals received by the analogue baseband chip are transferred to the digital baseband chip over a point-to-point serial link. That link is also used to transfer control data from the analogue baseband chip to the digital baseband chip.
Digital data to be transmitted in the form of a wireless signal is transmitted from the digital baseband chip to the analogue baseband chip over the link.
In addition, the processor may require access to data held on the analogue baseband chip, for example control data.
In essence, there are two classes of data that are transferred between the devices. “Ratio” data (which is converted to/from the radio signal and is a continual ordered stream) and control data (which is not continual and can be out-of-order).
Control data encompasses anything which is used to setup or monitor the analogue baseband system or radio system. Examples of analogue to digital baseband traffic are temperature monitoring, voltage monitoring, transmit power monitoring. Examples of digital to analogue baseband traffic are setup of the A/D and D/A converters and Tx power control.
The processor acts as a so-called soft modem, implementing signal processing by executing code sequences for signal detection, decoding etc. It is important therefore to keep the load of the processor for handling non-signal processing tasks to a minimum. In order to access data from the analogue baseband chip, the processor issues memory access requests which use up processing resource to issue and to handle the response.
A memory access request is transmitted over the serial link to the analogue baseband chip, and the data is returned from the memory location identified in the request. The processor must tag the requests and responses so they can be associated for further processing.